The present disclosure generally relates to liquid-filled cartridges and, in particular, to a liquid-filled cartridge having a piston wherein the piston moves inside a cartridge, to a system comprising the device as well as to a method using the cartridge.
A typical problem when dispensing or dosing a liquid from a cartridge, e.g. when dosing insulin from an insulin cartridge with an automated insulin pump, is not only to make sure that, for dispensing the liquid, the piston can be pushed forward inside the cartridge body in a controlled manner, but also that the piston cannot be sucked into the cartridge body by a pressure differential between the front and back side of the piston.
Furthermore, when filling the cartridge with a liquid from a liquid reservoir by retracting the piston inside the cartridge body, a further problem is to make sure that, even though a maximum stroke of the piston can be utilized, there is no risk that the piston will be drawn out of the cylinder body.
From the prior art, different approaches to solve these problems are known. For dispensing or dosing liquid from a cartridge or for filling a cartridge with a liquid by an automated device, it is known to fix the cartridge body inside the device and to connect the piston with a threaded connection to a piston rod of the device by which it can be pushed forward and/or be retracted in a controlled manner inside the cartridge body within the limits of its design stroke.
For manually filling cartridges or syringe assemblies, it is furthermore known to provide a physical stop for the piston at the end of the cartridge body or of the cylinder of the syringe assembly to prevent the piston from being drawn out of the cartridge body or syringe cylinder.
Furthermore, cartridges or syringe assemblies are known having a piston which provides, on its backside, moveable couplings which, in a positive manner, engage an especially adapted piston rod once this piston rod is pushed towards the backside of the piston and, once coupled to the piston rod, release the piston rod only in case they are retracted by the piston rod past a defined position within the cartridge body or syringe cylinder.
Furthermore, a cartridge is known having a piston which provides, on its backside, a threaded pin for coupling it to a piston rod. This threaded pin is formed by an element which is disconnected from the piston once the piston is retracted into a defined position within the cartridge body by a piston rod threaded onto the threaded pin.
However, the known solutions using a threaded connection for coupling the piston to a piston rod suffer from the disadvantage that they require a complex relative motion between the piston and the piston rod for establishing and releasing the connection, which is undesirable since it requires certain skills of the user or, in case of an automated device, a complex mechanical arrangement for controlling the motion of the piston rod. Also, there is the disadvantage that the quality of the connection to be established and the possibility to release it later on is influenced by the friction between the piston and the cartridge body or the syringe cylinder, since this friction defines the torque which can be applied to the threaded connection.
The solutions providing a physical stop for the piston at the end of the cartridge body or of the cylinder of the syringe assembly have the disadvantage that in the manufacturing of the cartridge or syringe assembly, additional operating steps are required, which increases the manufacturing costs.
The solutions providing moveable couplings at the backside of the piston which release the piston rod once the piston is retracted into a defined position or providing an element for connection with the piston rod which element is disconnected from the piston once the piston is retracted into a defined position have the disadvantage that the piston is of complex design and as a result is difficult to manufacture and expensive.
Additionally, all of the know solutions suffer from the disadvantage that they require relatively expensive cartridge or syringe assembly designs that reduce the attractiveness to use them in fields where the cartridge or syringe assembly should be an inexpensive single use article, like, for example, a self-filled insulin cartridge for the therapy of diabetes.
Therefore, there is a general need for improvements in this area.